Silica-alumina compounds are well known as catalysts used in hydrocarbon conversion processes. Silica/alumina catalysts such as in the present invention can be used “as is”, particularly in reactions that require acidic catalysts, or can optionally be combined with zeolites, clays or other binders, and inorganic oxides for the cracking of liquid hydrocarbons in cracking reactors such as fluid catalytic crackers and hydrocrackers. Silica-alumina composites have been used commercially for a variety of hydrocarbon processing applications, such as cracking, desulphurization, demetalation, and denitrification.
Amorphous silica-alumina has been prepared previously by a modified cogel process wherein no hydrogenation metals were added during the gellation step. Spray dried, amorphous silica-alumina catalysts were made by the method as described in U.S. Pat. No. 4,988,659, Pecoraro to produce catalysts used in hydrocarbon conversion processes.
The method of preparation of silica-alumina catalysts affects the chemical and physical properties of the catalysts such as activity (such as cracking or isomerization activity), and physical properties (such as pore structure and volume, surface area, density and catalyst strength). Silica-alumina catalysts such as in the present invention can be used “as is”, particularly in reactions that require acidic catalysts, or can optionally be combined with zeolites, clays or other binders, and inorganic oxides for the cracking of liquid hydrocarbons in cracking reactors such as fluid catalytic crackers.
Numerous silica-alumina catalyst compositions and processes for their preparation are described in the patent literature. The patent literature teaches a number of ways to prepare these compositions. U.S. Pat. No. 4,499,197, Seese et al., for example, describes the preparation of inorganic oxide hydrogels, and more particularly, catalytically active amorphous silica-alumina and silica-alumina rare earth cogels. The active cogels are prepared by reacting aluminate and silicate solutions to obtain a silica-alumina pregel, and then reacting the pregel with an acidic rare earth and an aluminum salt solution with complete mixing. U.S. Pat. No. 4,239,651, Alfandi et al., discloses a process for preparing exchanged ammoniated cogels.
U.S. Pat. No. 4,289,653, Jaffe teaches preparing an extruded catalyst by mixing aluminum sulfate and sulfuric acid with sodium silicate to form a silica sol in an alumina salt solution at pH of 1-3, adding NH4OH under substantially constant pH of at least 4 to 6; adding more NH4OH to form a cogelled mass to pH 7.5-8.5; washing cogelled mass; mulling the mass with peptizing agent, a Group VI-B metal compound and a Group VIII metal compound to form extrudable dough; extruding; and drying and calcining.
U.S. Pat. No. 4,988,659, Pecoraro teaches a cogelled, silica-alumina matrix prepared by the method which comprises mixing a silicate solution with an aqueous solution of an acid aluminum salt and an acid, to form an acidified silica sol in said aluminum salt solution, and adjusting said silica sol/aluminum salt solution mixture to a pH in the range of about 1 to 4; slowly adding sufficient base with vigorous stirring, to said acidified silica sol/aluminum salt solution mixture to form a cogel slurry of silica and alumina, and to adjust said slurry to a pH in the range of about 5 to 9; aging said cogel slurry at a temperature of ambient to 203° F.; adjusting the pH of said cogel slurry to about 5-9; recovering a cogelled mass from said slurry; washing said cogelled mass; adjusting the pH of said cogelled mass to between about 4 and 7, and controlling conditions to induce syneresis; and forming said combination into particles.